How It's Measured
The number beside the number
We measure the lap along the line it was surveyed, so you can check the print against the circuit's own figure. Here is how, and how close it comes.
Our length beside theirs
- Monza, measured
- 5.798 km
- The circuit publishes
- 5.793 km
- Difference
- 5 m longer
- Turns, as Monza numbers them
- 11
- Corners, as we count them
- 10
- Longest straight
- 1,266 m
An outline without its length is a logo, and the logo belongs to the circuit. The measurement is what makes the print yours. We measure the lap along the centreline OpenStreetMap's volunteers drew, so you can check the print against the circuit's own figure, and where the two disagree the table below says by how much.
5.793 km published, 5.798 km measured at Monza; of our 25 circuits, the 20 that publish a length all land within the margin set beside each.
How do you find the lap?
The closed loop through the circuit's raceway ways with the greatest length.
OpenStreetMap's volunteers draw a circuit as a set of ways tagged as raceway. We join them where they share a point and look for the longest loop, every one-way way driven its own way. A way named for another layout or another sport counts for less; a way the mappers mark as the international or national layout counts for more. A corner's own name is never taken for a layout's.
How is the length measured?
Point to point on the WGS84 ellipsoid, with Vincenty's formulae.
Our implementation is tested against C. F. F. Karney's test set for geodesics to a millimetre. The lap is then resampled every 2 m to find its corners and straights.
What counts as a corner?
A change of heading over 25 degrees within 40 m.
Corners are numbered from the start/finish line in the direction of travel. A circuit numbers its own turns by committee, and some count a sequence of bends as one, so our count can differ from theirs; the table below shows where.
Where is the start/finish line?
Where the mappers put it, or beside the middle of the pit lane.
Most circuits have no start/finish line mapped. Then we place it on the lap beside the middle of the pit lane, and with no pit lane, in the middle of the longest straight. The print's margin says which rule placed it.
How close is it?
20 of the 20 circuits on this site with a published length land inside our tolerance.
The tolerance is the larger of 2 % and 60 m, written into our tests before the first comparison ran and never loosened. A circuit outside it stays in the table, with the miss named.
| Circuit | Ours | Theirs | Difference | Tolerance | Verdict |
|---|---|---|---|---|---|
| Monza | 5,798 m | 5,793 m | +5 m | 116 m | within |
| Brands Hatch | 3,903 m | 3,915.5 m | -12.5 m | 78 m | within |
| Spielberg | 4,373 m | 4,326 m | +47 m | 87 m | within |
| Imola | 4,938 m | 4,909 m | +29 m | 98 m | within |
| Mugello | 5,246 m | 5,245 m | +1 m | 105 m | within |
| Hungaroring | 4,372 m | 4,381 m | -9 m | 88 m | within |
| Catalunya | 4,727 m | 4,657 m | +70 m | 93 m | within |
| Portimão | 4,679 m | 4,684 m | -5 m | 94 m | within |
| Donington Park | 4,006 m | 4,007.3 m | -1.3 m | 80 m | within |
| Lime Rock | 2,414 m | 2,414 m | 0 m | 60 m | within |
| Interlagos | 4,322 m | 4,309 m | +13 m | 86 m | within |
| Suzuka | 5,820 m | 5,807 m | +13 m | 116 m | within |
| Fuji | 4,553 m | 4,563 m | -10 m | 91 m | within |
| Sepang | 5,542 m | 5,543 m | -1 m | 111 m | within |
| Phillip Island | 4,452 m | 4,445 m | +7 m | 89 m | within |
| Circuit Gilles Villeneuve | 4,363 m | 4,361 m | +2 m | 87 m | within |
| Assen | 4,556 m | 4,542 m | +14 m | 91 m | within |
| Motegi | 4,812 m | 4,800 m | +12 m | 96 m | within |
| Oulton Park | 4,325 m | 4,329.1 m | -4.1 m | 87 m | within |
| Snetterton | 4,800 m | 4,828 m | -28 m | 97 m | within |
Our corners beside theirs
9 of the 14 circuits that publish a turn count land within 2 corners of ours, a margin set before the first comparison ran and never loosened. A circuit outside it stays in the table, with the miss named. The other 11 publish no count, and their pages show ours alone.
| Circuit | Ours | Theirs | Difference | Verdict |
|---|---|---|---|---|
| Monza | 10 | 11 | -1 | within |
| Brands Hatch | 13 | 11 | +2 | within |
| Spielberg | 11 | 10 | +1 | within |
| Hungaroring | 13 | 14 | -1 | within |
| Catalunya | 23 | 14 | +9 | outside: kept, named |
| Portimão | 14 | 16 | -2 | within |
| Donington Park | 10 | 12 | -2 | within |
| Interlagos | 15 | 11 | +4 | outside: kept, named |
| Suzuka | 20 | 18 | +2 | within |
| Fuji | 14 | 17 | -3 | outside: kept, named |
| Sepang | 14 | 15 | -1 | within |
| Motegi | 14 | 14 | 0 | within |
| Oulton Park | 14 | 17 | -3 | outside: kept, named |
| Snetterton | 17 | 12 | +5 | outside: kept, named |
Why is our length longer than theirs, or shorter?
Because we measure the mapped centreline, and they may not.
A circuit may publish the racing line, a line a metre from the pit wall, or a layout changed since it was mapped, so the two figures can differ by tens of metres. Some round to the nearest 100 m, and then we say the difference sits inside the rounding instead of quoting a number we can't stand behind.
Where do the heights come from?
Public elevation tiles, about 4 m to a pixel.
AWS Terrain Tiles, from 3DEP, SRTM and other surveys. A crest the size of a car doesn't show; a hill the size of a whole corner sequence does.
Why isn't my circuit's lap closing?
Because a piece of it is missing from the map.
Anyone can add it. Open the circuit on openstreetmap.org, draw the missing piece of track as a way tagged highway=raceway, joined at both ends, and the studio finds the lap the next time it asks.